Peter A. Summers

Remote-controlled experiments with cloud chemistry

Developing cleaner chemical processes often involves sophisticated flow-chemistry equipment that is not available in many economically developing countries. For reactions where it is the data that are important rather than the physical product, the networking of chemists across the internet to allow remote experimentation offers a viable solution to this problem.

From waste plastics to industrial raw materials: A life cycle assessment of mechanical plastic recycling practice based on a real-world case study

Mechanical recycling of waste plastics is an environmental solution to the problem of waste plastic disposal, and has already become a common practice in industry. However, limited information can be found on either the industralised plastic recycling or the recycled materials, despite the use of recycled plastics has already extended to automobile production. This study investigates the life cycle environmental impacts of mechanical plastic recycling practice of a plastic recycling company in China. Waste plastics from various sources, such as agricultural wastes, plastic product manufacturers, collected solid plastic wastes and parts dismantled from waste electric and electronic equipments, are processed in three routes with products end up in different markets. The results of life cycle assessments show that the extrusion process has the largest environmental impacts, followed by the use of fillers and additives. Compared to production of virgin plastics and composites, the mechanical recycling is proved to be a superior alternative in most environmental aspects. Substituting virgin plastic composites with recycled plastic composites has achieved the highest environmental benefits, as virgin composite production has an impact almost 4 times higher that of the recycled composite production in each ReCiPe endpoint damage factor. Sensitivity analysis shows that the coverage of collecting network contribute affect little to overall environmental impact, and centralisation plays an important role in reducing overall environmental impacts. Among the fillers and additives, impact modifiers account for the most significant contributions to the environmental impacts of recycled composites. This study provides necessary information about the existing industrialised plastic recycling practice, and recommendations are given. Research implications are presented with the purpose to achieve higher substitution rate and lower environmental impact.

Photochemical Dihydrogen Production Using an Analogue of the Active Site of [NiFe] Hydrogenase

Photoproduction of dihydrogen (H2) by a low molecular weight analogue of the active site of [NiFe] hydrogenase has been investigated by reduction of the [NiFe2] cluster, 1, by a photosensitier PS (PS = [ReCl(CO)3(bpy)] or [Ru(bpy)3][PF6]2). Reductive quenching of the (3)MLCT excited state of the photosensitizer by NEt3 or N(CH2CH2OH)3 (TEOA) generates PS(•-), and subsequent intermolecular electron transfer to 1 produces the reduced anionic form of 1. Time-resolved infrared spectroscopy (TRIR) has been used to probe the intermediates throughout the reduction of 1 and subsequent photocatalytic H2 production from [HTEOA][BF4], which was monitored by gas chromatography. Two structural isomers of the reduced form of 1 (1a(•-) and 1b(•-)) were detected by Fourier transform infrared spectroscopy (FTIR) in both CH3CN and DMF (dimethylformamide), while only 1a(•-) was detected in CH2Cl2. Structures for these intermediates are proposed from the results of density functional theory calculations and FTIR spectroscopy. 1a(•-) is assigned to a similar structure to 1 with six terminal carbonyl ligands, while calculations suggest that in 1b(•-) two of the carbonyl groups bridge the Fe centers, consistent with the peak observed at 1714 cm(-1) in the FTIR spectrum for 1b(•-) in CH3CN, assigned to a ν(CO) stretching vibration. Formation of 1a(•-) and 1b(•-) and production of H2 was studied in CH3CN, DMF, and CH2Cl2. Although the more catalytically active species (1a(•-) or 1b(•-)) could not be determined, photocatalysis was observed only in CH3CN and DMF.

Synthesis and Photophysical Study of a [NiFe] Hydrogenase Biomimetic Compound Covalently Linked to a Re-diimine Photosensitizer.

The synthesis, photophysics, and photochemistry of a linked dyad ([Re]-[NiFe2]) containing an analogue ([NiFe2]) of the active site of [NiFe] hydrogenase, covalently bound to a Re-diimine photosensitizer ([Re]), are described. Following excitation, the mechanisms of electron transfer involving the [Re] and [NiFe2] centers and the resulting decomposition were investigated. Excitation of the [Re] center results in the population of a diimine-based metal-to-ligand charge transfer excited state. Reductive quenching by NEt3 produces the radically reduced form of [Re], [Re]− (kq = 1.4 ± 0.1 × 107 M–1 s–1). Once formed, [Re]− reduces the [NiFe2] center to [NiFe2]−, and this reduction was followed using time-resolved infrared spectroscopy. The concentration dependence of the electron transfer rate constants suggests that both inter- and intramolecular electron transfer pathways are involved, and the rate constants for these processes have been estimated (kinter = 5.9 ± 0.7 × 108 M–1 s–1, kintra = 1.5 ± 0.1 × 105 s–1). For the analogous bimolecular system, only intermolecular electron transfer could be observed (kinter = 3.8 ± 0.5 × 109 M–1 s–1). Fourier transform infrared spectroscopic studies confirms that decomposition of the dyad occurs upon prolonged photolysis, and this appears to be a major factor for the low activity of the system toward H2 production in acidic conditions.

Molecular catalysts for artificial photosynthesis: general discussion

Mei Wang, Vincent Artero, Leif Hammarström, Jose Martinez, Joshua Karlsson, Devens Gust, Peter Summers, Charles Machan, Peter Brueggeller, Christopher D. Windle, Yosuke Kageshima, Richard Cogdell, Kristine Rodulfo Tolod, Alexander Kibler, Dogukan Hazar Apaydin, Etsuko Fujita, Johannes Ehrmaier, Seigo Shima, Elizabeth Gibson, Ferdi Karadas, Anthony Harriman, Haruo Inoue, Akihiko Kudo, Tomoaki Takayama, Michael Wasielewski, Flavia Cassiola, Masayuki Yagi, Hitoshi Ishida, Federico Franco, Sang Ook Kang, Daniel Nocera, Can Li, Fabio Di Fonzo, Hyunwoong Park, Licheng Sun, Tohru Setoyama, Young Soo Kang, Osamu Ishitani, Jian-Ren Shen, Ho-Jin Son and Shigeyuki Masaoka

Inorganic assembly catalysts for artificial photosynthesis: general discussion

Hiromu Kumagai, Leif Hammarström, Dong Ryeol Whang, Yuki Shinohara, Jose Martinez, Joshua Karlsson, Peter Summers, Christopher D. Windle, Masanori Kodera, Richard Cogdell, Kristine Rodulfo Tolod, Dogukan Hazar Apaydin, Etsuko Fujita, Alexander Kibler, Fengtao Fan, Elizabeth A. Gibson, Hisanao Usami, Akihide Iwase, Haruo Inoue, Akihiko Kudo, Devens Gust, Kazunari Domen, Flavia Cassiola, Katsuhiko Takagi, Sang Ook Kang, Akira Yamakata, Can Li, Licheng Sun, Hyunwoong Park, Young Soo Kang, Rengui Li, Fabio Di Fonzo, Tohru Setoyama and Osamu Ishitani